High power radar

[engguy]

I just did a search on this topic, and pretty much got nothing. Where is a good site about all the latest in radar tech, well and the old stuff as well?

[Wavelength]

http://www.cdvandt.org/Fug200-paper-Hans-Jucker.pdf

The Hohentwiel radar design referred to in the article obtained relatively high pulse power by delivering a high voltage pulse to the anode of the transmitting tube, via a high voltage pulser such as a thyratron. This was the way to high pulse powers during WWII.

Normally, a lower power pulse was delivered to the control grid of a triode, but this limited radiated power. For example, the German Freya air warning radar delivered a precisely timed and shaped low powered pulse to the control grid of the transmitting triode. This created a radiated power of about 35kw using grid modulation of the late war TS41 transmitting triode, but by using anode modulation the radiated power output was increased to 200kw. Increasing the pulse voltage from a spark gap pulser resulted in power outputs for Freya exceeding 1000kw. Anode modulation does create certain problems, such long warm up times, and poor pulse shape. Random timing of the pulses is also a problem, making coherent radar techniques problematic.

Another way to effective high power is not through high pulse power per se, but through longer pulse widths. The illumination energy delivered to the target is the radiated pulse power multiplied by the pulse duration. For example, the 50kw ship board Hohentwiel alluded to in the Junker article would have illumination energy, of 100kw because it uses a 2 microsecond pulse width. The longer the pulse width; the lesser the bandwidth requirement of the receiver. This results in a more sensitive receiver with a far superior signal to noise ratio.

High illumination energy combined with a more sensitive receiver can result in excellent performance. This is the typical approach used by modern solid state radar designs. The trade off, with out the use of coherent radar techniques, is very poor resolution for distance. Modern coherent radar techniques such as pulse compression and other types of pulse modulated radar can get excellent resolution performance while still using long pulse widths, but they must also use very high bandwidth at the receiver while employing greatly compressed pulse widths.